Poor pre-bunker checklist contributes to HSFO overflow

In its latest Safety Digest, the UK MAIB described an incident of a Heavy Sulphur Fuel Oil overflow during bunkering operation. MAIB highlighted that at least one of the two isolating valves that caused the incident could have been closed fully if it had been checked as per the checklist.

An LPG carrier was at anchor awaiting a berth when instructions to take bunkers were received. A bunkering plan was completed by the ship’s crew prior to the bunker barge arriving alongside.

A pre-bunker meeting was held with the barge representative and ship’s crew and it was agreed to bunker low sulphur marine gas oil (LSMGO) first followed by high sulphur fuel oil (HSFO). A verbal ‘stop’ instruction was agreed as the emergency stop signal, with two-way communication maintained on a dedicated VHF radio channel.

The valves were aligned for receiving LSMGO and the transfer was commenced, completing about an hour later with the hose being disconnected. The HSFO hose was then connected and the bunker plan and checklist completed. The valves were lined up to receive HSFO into two tanks simultaneously, and pumping was started.

An hour later, the deck watch sighted oil overflowing from the vents of the overflow tank and another tank that was not supposed to be receiving any HSFO. The order to stop bunkering was given and the vessel’s emergency response team was activated, but they were unable to prevent HSFO escaping overboard through a freeing port.

Roughly 1 tonne of HSFO was recovered from on deck, and six drums of contaminated soak up material was discharged to the garbage boat. Although difficult to estimate, up to 2000 litres of HSFO were lost overboard.

It was subsequently discovered that two valves aligned to another fuel tank were not fully closed. One valve was jammed with some debris and the other not fully tightened, which allowed fuel to flow into a tank that was already 80% full, eventually causing it to overflow.

Lessons learned

Remain disciplined, and don’t get into a ‘tick box’ mentality when completing checklists. Make sure that the items on the checklist have been completed. In this case, one of the two isolating valves could have been closed fully if it had been checked.

It is vital that all tank levels, as well as the tanks being filled, are monitored during bunkering to check that fuel is flowing as intended. Don’t assume because a valve appears shut that it is holding.

In this instance, the bunker tank high level alarm (90%) and overflow tank (10%) sounded in the engine room and engine control room. Both were acknowledged but no action was taken by the crew. Two vital indicators that something was wrong were ignored. Clear communications and instructions are essential to ensure crew have a common understanding of the operation and the role they play.

The deck included freeing ports to allow water to be readily shipped overboard. However, there was no means of closing off the freeing ports during cargo/ bunkering operations. This simple last line of defence could have prevented polluting the marine environment and the extensive clean-up operation that subsequently took place.